Prove that: `inttan^n x\ dx=1/(n-1)tan^("n"-1)x-inttan^(n-2)x\ dx`

Explanation

To prove the recurrence relation for the integral of \( \tan^n x \), we need to show that:

\[ \int \tan^n x \, dx = \frac{1}{n-1} \tan^{n-1} x - \int \tan^{n-2} x \, dx \]

### Step 1: Start with the integral
Let \( I_n = \int \tan^n x \, dx \).
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